Vinyl resins, such as polyvinyl chloride (PVC) and certain copolymers of vinyl halides, represent a highly versatile class of synthetic resins which can be processed by various methods into a myriad of useful end products. In order to facilitate end-use processing, it is the usual practice in the art to design the vinyl resins for use in specific processing techniques. As a result, such designing necessarily requires adjusting the balance of the vinyl resin properties in order to enhance those which are desirable or necesssary for the intended end use of the particular vinyl resin being made.
It is known that vinyl resins may be plasticized or changed from the hard, horny and stiff state to a soft, plastic workable condition by the addition thereto at elevated temperatures of certain plasticizers, such as dioctyl phthalate, for example. When the vinyl resin is so mixed or blended with a plasticizer, it is referred to as a "plastisol" and by virtue of the flowability thereof, it can be processed into various useful products, such as molded products, coatings, and the like. The vinyl resin must be capable of being mixed with a plasticizer easily and uniformly to form low viscosity plastisols which are stable, containing particles of uniform and proper size, and capable of producing films and like products, of good clarity. It is often desirable to maximize the ability of the vinyl resins to absorb and/or to adsorb plasticizers in order to facilitate and increase their use in the manufacture of certain end products, such as, for example, flexible films and sheeting, and particularly for use in the flooring or floor-covering industry.
Various processes have heretofore been prepared and employed in order to attain vinyl plastisol resins with high plasticizer capacity and having increased flexibility, workability and dispensibility. Chief among these processes have been the customary emulsion polymerization processes. However, suitable plastisol resins have been difficult to obtain via this route since the latices produced thereby contain polymer particles of varying size, the majority of which are either too fine or too large. The aqueous suspension polymerization technique has been employed in making vinyl plastisol resins or polymers but the same has resulted in the generation of very fine resin particles or "fines" which results in the inconvenient and detrimental creation of polymer dust. These fines hamper the pneumatic bulk handling of the vinyl resins and also create potential health hazards, that is, enough of the fines pass out in the plant effluent to put said plant out of compliance with the Environmental Protection Agency (EPA) requirements. More importantly, from a technical and business point of view, the use of many of the prior processes in making vinyl plastisol resins has resulted in drastic losses in the bulk density and heat stability of the resins, which in turn makes them unsuitable for many end uses and creates costly problems in handling and storage of such resins.
Accordingly, there is a need in the art for a process for producing vinyl plastisol resins which overcomes the aforementioned difficulties and is a convenient, inexpensive process which produces resins which retain the desirable properties ordinarily found in conventional or general purpose resins.